technology brief ethernet ring protection switching (erps) april. 2010 d-link hq

Technology Brief

Ethernet Ring Protection Switching

(ERPS)

April. 2010

D-Link HQ

Agenda

What is ERPS ?

Drivers for ERPS

ERPS Technology

Benchmarking

ERPS CLI commands

Hands-on configuration

Application Examples

ERPS (Ethernet Ring Protection Switching) is the first industry standard

(ITU-T G.8032) for Ethernet ring protection switching.

It is achieved by integrating mature Ethernet operations, administration,

and maintenance (OAM) * functions and a simple automatic protection

switching (APS) protocol for Ethernet ring networks.

It provides sub-50ms protection for Ethernet traffic in a ring topology.

It ensures that there are no loops formed at the Ethernet layer.

The first version supported a single ring architecture and the second

version is expected to address multiple inter-connected rings.

What is ERPS ?

* Please refer to the document – “Technology Brief-Ethernet OAM”.

Link Down!

Link Down!

Disable Blocking

Aggregation Ring

Access Ring

ERPS Scenario

Use a ring topology for the Ethernet traffic.

One link within a ring will be blocked to avoid Loop (called RPL: Ring Protection Link) .

When the failure happens, protection switching blocks the failed link and unblocks the RPL.

When the failure clears, protection switching blocks the RPL again and unblocks the link on which the failure is cleared.

RPL

RPL

* The slide is animated.

Agenda

What is ERPS ?

Drivers for ERPS

ERPS Technology

Benchmarking

ERPS CLI commands



Ethernet Technology Development

•Ethernet as a carrier-class technology continues to make considerable

progresses within carrier networks.

•According to a recent market study report, over 75% of respondents have a

strategy of using Ethernet instead of SDH or SONET for accessing and

transmitting customer traffic.

• The Ethernet bandwidth-cost merits increase rapidly with 1GbE, 10GbE,

100GbE, etc., due to its commoditization.

Drivers for ERPS

Ring’s Application for Service Provider

•The ring topology is considered the simplest redundant topologies and are often implemented in

Metropolitan Ethernet Networks (Metro) to minimize optical fiber usage.

•Effective means of aggregating DSLAMs or small Ethernet switches in multi-tenant or multi-dwelling

environments in Metro access networks

•To support video and voice services for their triple-play deployments, service providers require fast

and predictable convergence time.

Drivers for ERPS

Drawbacks of STP – The convergence time is too long!

• STP (spanning-tree protocol) is built for the redundant links and loop

avoidance network. When topology changes, STP takes about 30-50

seconds to converge.

• RSTP (Rapid STP) improves the speed of convergence for bridged network

from 30-50 seconds to about 4 seconds, by immediately transitioning root

and designated ports to the forwarding state.

• ERPS only spends 50-200 ms converging but it uses a ring topology

instead of tree topology.

Drivers for ERPS

STP RSTP ERPS

Topology Type Any Topology Any Topology Ring Topology

Convergence Time 30-50 seconds 4 seconds 50-200ms*

Agenda

What is ERPS ?

Drivers for ERPS

ERPS Technology

Benchmarking

ERPS CLI commands



ERPS must support Ethernet ring topology as below:Single ring (a)

Two single-rings with a shared node (b)

Multi-ring: Rings share common link and nodes (c)

Nested multi-ring in a ladder topology (d)

Each ring node has two ring ports per ring and all nodes can be connected in a physically closed loop.

A physical ring will maintain a logical (non-looping) linear MAC topology with one link blocked.

Ring Topology

Use of standard 802 MAC and OAM frames around the ring. Uses standard

802.1Q (and amended Q bridges), but with xSTP disabled.

Ring nodes support the standard FDB (forwarding database) MAC learning,

forwarding, flushing behavior and port blocking/unblocking mechanisms.

A ring node with a blocked port (either a pre-determined link or a failed link)

prevents R-APS massages received at one port from being forwarded to the

other ring port.

The ring protection link(RPL) is the ring link which under normal conditions is

blocked (at one end or both ends) for traffic channel, to prevent loops.

Monitoring of the ETH layer for discovery and identification of Signal Failure

(SF) conditions.

Protection and recovery switching is within 50 ms for typical rings.

G.8032 Objectives and Principles

RPL (Ring Protection Link) – Link designated by mechanism that is blocked

during Idle state to prevent loop on Bridged ring

RPL Owner – Node connected to RPL that blocks traffic on RPL during Idle state

and unblocks during Protected state

R-APS (Ring – Automatic Protection Switching) - Protocol messages

defined in Y.1731 and G.8032 used to coordinate the protection actions over

the ring through RAPS VLAN (R-APS Channel).

R-APS Message

Signal Fail (SF) – Signal Fail is declared when ETH trail signal fail condition is detected

No Request (NR) – No Request is declared when there are no outstanding conditions

(e.g., SF, etc.) on the node

RPL Blocked (RB) – RPL Blocked is declared by RPL Owner; it always comes with NR.

G.8032 Terms and Concepts

* Please refer to Appendix for R-APS packet format and R-APS process.

RAPS VLAN (R-APS Channel) – A separate ring-wide VLAN for transmission of R-

APS messages

Protected VLANs – The service traffic VLANs for transmission of normal network

traffic

The ERP (Ethernet Ring Protection) Control process controls forwarding of service

traffic and R-APS protocol messages.

R-APS Channel & ERP Control

R-APS forwarding

(RAPS VLAN) Service traffic forwarding

(Protected VLANs)

ERP Control

WEST LINK EAST LINK

Exterior of ring

Model of a ring node with its port blockedBlocking by ERP Control

Node

RPL

* The slide is animated.

Three node states –

Initialization – when first defining the ring

Idle – the ‘normal’ state of the ring nodes with RPL blocked and all nodes/ports

working

Protecting – when protection switching is in effect, RPL unblocked, other (usually

fault) link is blocked.

State Machine describes the actions to be taken by the node dependent on current state and input message.*

Protection switching triggered by

• Detection/clearing of Signal Failure (SF) by ETH CC (Continuity Check) OAM

messages

• Remote requests over R-APS channel (using Y.1731 protocol)

• Expiration of G.8032 timers (WTR or hold-off timer)

Node States and Switching Triggers

* Please refer to Appendix.

R-APS control the communication and states of the ring nodes

•Two basic R-APS messages specified - R-APS(SF) and R-APS(NR)

•RPL Owner may modify the R-APS(NR) to R-APS(NR,RB) indicating the RPL is

blocked

Different actions include – transmission of R-APS message,

blocking/unblocking a port, flushing the FDB, switching current state of

node, and starting/stopping timers.

FDB flushing will clear all of the learned MAC addresses of the ring ports

from the forwarding database (FDB).

The Protection Mechanism

G.8032 specifies the use of different timers to avoid race

conditions and unnecessary switching operations

•Hold-off Timers – Used by underlying ETH layer to filter out intermittent link

faults ; Faults will only be reported to the ring protection mechanism if this

timer expires

•WTR (Wait to Restore) Timer –When the failed link recovered, this is Used by

the RPL Owner to verify that the ring has stabilized before restoring the ring

(blocking the RPL).

•Guard Timers – Used to prevent ring nodes from receiving outdated R-APS

messages. During the duration of the guard timer, all received R-APS messages

are ignored by the ring protection control process. *

Timers

* Please refer to Appendix to see the guard timers function inR-APS process.

Physical topology has all nodes

connected in a ring

ERP guarantees lack of loop by blocking

the RPL (link between 6 & 1 in figure)

Logical topology has all nodes

connected without a loop.

Each link is monitored by its two

adjacent nodes using ETH CC OAM

messages

Signal Failure as defined in Y.1731, is

triggered to ring protection

• Loss of Continuity

• Server /Physical layer failure

RPL Owner

RPL

ETH-CC

ETH-CC

ETH-CC

ETH-CC

ETH-CC

ETH-CC

ETH-CC

ETH-CC

ET

H-C

C

ET

H-C

C

ET

H-C

C

ET

H-C

C

Physical topology

Logical topology

12 6

43 5

RPL

12 6

43 5

Ring Idle State (Normal Condition)

Link/node failure is detected by the

nodes adjacent to the failure.

The nodes adjacent to the failure

block the failed link and report this

failure to the ring using R-APS (SF)

message

R-APS (SF) message triggers

• RPL Owner unblocks the RPL

• All nodes perform FDB flushing

Ring is in protection state

All nodes remain connected in the

logical topology.

Physical topology

Logical topology

12 6

43 5

RPL12 6

43 5

RPL

12 6

43 5

12 6

43 5

RPL Owner

RPL

R-APS(SF) R-APS(SF)

R-APS(SF)

R-A

PS

(SF)

Link Failure

* The slide is animated.* Please refer to Appendix for detailed process.

When the failed link recovers, the traffic is kept blocked on the nodes adjacent to the recovered link

The nodes adjacent to the recovered link transmit R-APS(NR) message indicating they have no local request present

When the RPL Owner receives R-APS(NR) message it Starts WTR timer

Once WTR timer expires, RPL Owner blocks RPL and transmits R-APS (NR, RB) message

Nodes receiving the message – perform a FDB Flush and unblock their previously blocked ports

Ring is now returned to Idle state

RPL Owner

RPL

R-APS(NR) R-APS(NR)

R-APS(NR)

R-A

PS

(NR

)

R-APS(NR, RB)

R-A

PS

(NR

, RB

)

Physical topology

Logical topology

12 6

43 5

RPL

12 6

43 5

12 6

43 5

RPL

12 6

43 5

Failure Recovery

* The slide is animated.* Please refer to Appendix for detailed process.

Agenda

What is ERPS ?

Drivers for ERPS

ERPS Technology

Benchmarking

ERPS CLI commands



Company D-Link Cisco 3 COM Foundry HP Extreme Allied Telesis

Protocol ERPS(ITU-T

G.8032)

REP RRPP MRP/ MRPII

RRPP EAPS(RFC-3619)

EPSR

Name Ethernet Ring

Protection Switching

Resilient Ethernet Protocol

Rapid Ring

Protection Protocol

Metro Ring

Protocol

Rapid Ring

Protection Protocol

Ethernet Automatic Protection Switching

Ethernet Protection Switching

Ring

Ring Topologies

Single ring/ Multiple rings

Single ring/ More

complex rings

Single ring/Two or

more rings

Single ring/Overlapping

rings

Single ring/Two or

more rings

Single rings Single ring

Convergence Time

50-200ms 50-250ms < 200ms 50ms < 200ms Faster than

RSTP

50ms

Benchmarking

DES-3028/52 Series R3

DES-3528/52 Series R3

DES-3810 Series R1

DGS-3400 Series R3

DGS-3600 Series R2.8

DGS-3700 Series R2

D-Link Products support ERPS

Agenda

What is ERPS ?

Drivers for ERPS

ERPS Technology

Benchmarking

ERPS CLI commands



ERPS CLI Command

Enable the global ERPS function on a switch.

enable erps

disable erps

Disable the global ERPS function on a switch.

Create ring automatic protection switching (R-APS) vlan. The switch uses the

R-APS protocol to coordinate the switching behavior through this vlan ( APS

Channel ) with other ring switches.

create erps raps_vlan <vlanid>

config erps raps_vlan <vlanid> ring_mel <value 0-7>

Configure the MEL value of the ERPS ring for a specific R-APS VLAN

ERPS CLI Command

config erps raps_vlan <vlanid> ring_port [west <port> | east <port>]

Configure the ports connecting to the ERPS ring for a specific R-APS VLAN

There are “west” and “east” ring ports of the switch to the ring.

Configure the RPL port for a specific R-APS VLAN.

config erps raps_vlan <vlanid> rpl_port [west|east|none]

config erps raps_vlan <vlanid> rpl_owner [enable|disable]

Configure the RPL owner for a specific R-APS VLAN.

config erps raps_vlan <vlanid> protected_vlan [add|delete] vlanid <vidlist>

Configure the protected VLAN for a specific R-APS VLAN.

“protected_vlan” is used to configure the VLANs of the (service) traffic channel that

are protected by the ERPS function.

ERPS CLI Command

Configure the ERPS timers for a specific R-APS VLAN.

config erps raps_vlan <vlanid> timer { holdoff_time <value 0 - 10000> |

guard_time <value 10 - 2000 > | wtr_time <value 5 - 12>}]

Display ERPS configuration and operation information.

show erps {raps_vlan <vlanid> {sub_ring}}

config erps trap [enable | disable]

Configure the trap state of the ERPS.

config erps raps_vlan <vlanid> state [enable | disable]

Configure the state of the specified ring.

Agenda

What is ERPS ?

Drivers for ERPS

ERPS Technology

Benchmarking

ERPS CLI commands



Internet

(A) DES 3052

(B) DES 3052P

1

2

Ring connection port 4(A) to port 3(B)

Ring connection port 3(A) to port 4(B)

DPH-125MS

DPH-125MS

UPLINK DVX-2000MS

Hands-on Configuration SampleTesting Scenario I Topology

RPL Owner

P3: West P4: East

P4: East P3: West

Testing Scenario I Topology

Set Switch A to be RPL Owner

config serial_port auto_logout never

create vlan vlanid 3

config vlan vlanid 3 add tagged 3-4

create erps raps_vlan 3

config erps raps_vlan 3 ring_port west 3

config erps raps_vlan 3 ring_port east 4

config erps raps_vlan 3 protected_vlan add vlanid 1

config erps raps_vlan 3 rpl_port west

config erps raps_vlan 3 rpl_owner enable

enable erps

Hands-on Configuration Sample

Set Switch B to be a regular switch

config serial_port auto_logout never

create vlan vlanid 3






config erps raps_vlan 3 rpl_port none

enable erps


Switch A

DES-3052:4#show erps

Command: show erps

ERPS Information

---------------------------

ERPS Status : Enabled

R-APS VLAN : 3

West Port : 3 (Signal Fail Blocked)

East Port : 4 (Forwarding)

RPL port : west port

RPL owner : Yes

Protection VLANs : 1

Ring MEL : 1

Holdoff time : 0 ms

Guard time : 500 ms

WTR time : 5 minutes

Log : Disabled

Current Ring State : Protection


Switch B

DES-3052P:4#show erps

Command: show erps

ERPS Information

---------------------------


R-APS VLAN : 3

West Port : 3 (Forwarding)

East Port : 4 (Signal Fail)

RPL Port : None

Owner : Disabled


Ring MEL : 1

Holdoff Time : 0 ms

Guard Time : 500 ms

WTR Time : 5 minutes

Log : Disabled


Internet

DPH-125MS

DPH-125MS

DVX-2000MS

(A) DES 3052P

Ether Ring Connection

(D) DES 3052

(C) DES 3052P

(B) DES 3052

Testing Scenario II Topology

RPL Owner

P4: East

P4: East

P4: East

P4: East

P3: West

P3: West

P3: West

P3: West

Testing Scenario II Topology

Set Switch A to be RPL Owner create vlan vlanid 3






config erps raps_vlan 3 rpl_port west

config erps raps_vlan 3 rpl_owner enable

enable erps

Set Switch B to be a regular switch create vlan vlanid 3







enable erps

Set Switch C to be a regular switch create vlan vlanid 3







enable erps

Set Switch D to be a regular switch create vlan vlanid 3







enable erps


Switch A


Command: show erps

ERPS Information

---------------------------


R-APS VLAN : 3

West Port : 3 (Signal Fail Blocked)


RPL port : west port

RPL owner : Yes


Ring MEL : 1

Holdoff time : 0 ms

Guard time : 500 ms

WTR time : 5 minutes

Log : Disabled



Switch B


Command: show erps

ERPS Information

---------------------------


R-APS VLAN : 3


East Port : 4 (Signal Fail)

RPL Port : None

Owner : Disabled


Ring MEL : 1

Holdoff Time : 0 ms

Guard Time : 500 ms


Log : Disabled



Switch C


Command: show erps

ERPS Information

---------------------------


R-APS VLAN : 3



RPL Port : None

Owner : Disabled


Ring MEL : 1

Holdoff Time : 0 ms

Guard Time : 500 ms


Log : Disabled



Switch D


Command: show erps

ERPS Information

---------------------------


R-APS VLAN : 3



RPL Port : None

Owner : Disabled


Ring MEL : 1

Holdoff Time : 0 ms

Guard Time : 500 ms


Log : Disabled


Agenda

What is ERPS ?

Drivers for ERPS

ERPS Technology

Benchmarking

ERPS CLI commands



Access

Aggregation

Core

DGS-3612/27G/50

IPTV Partner

VoIP Partner

Internet InternetDGS-8000

DGS-3700-12GNew!

DES-3526/50DES-3028/52

DES-3200-10/18/28

Coming Soon!

Core Level Ring Protection Aggregation Level Ring Protection Access Level Ring Protection

ETTx Solution

Future

Aggregation

Access

Core

DGS-3612/27G

DGS-8000/DGS-6600

DES-3528/52

DGS-3612/27G

Campus Core Ring Protection Aggregation devices connect to the nodes in core Ring (Optional) Access Ring Protection. Usually for long distance, sparse deployment

Campus Solution

Future

Appendix

Protection switching algorithm is based on priorities assigned to all triggers. When a ring node has multiple outstanding requests, it only responds to the one with highest priority.

Ring Protection Requests Priority

Request Type Priority

Local SF Local highest

Local Clear SF Local

R-APS (SF) Remote

WTR Expires Local

WTR Running Local

R-APS (NR, RB) Remote

R-APS (NR) Remote lowest

State Machine

Inputs Outputs

Node State

High Priority request

Row#

Actions Next state

B

(Pro-tecting)

Local SF 8 Block failed port;Unblock non Failed port;Stop WTR;

Tx R-APS(SF);

B

Local Clear SF

9 Start guard timer,Tx R-APS(NR),

B

R-APS(SF) 10 Stop WTR,Unblock non Failed port,Stop Tx R-APS

B

WTR Expires

11 Block RPL port,Unblock non-RPL port

Tx R-APS (NR,RB)

Flush FDB,

A

WTR Running

12 No action B

R-APS(NR, RB)

13 If not RPL Owner:

Unblock both ports,

Stop Tx R-APS,

If not “DNF” Flush FDB

A

R-APS(NR) 14 If RPL Owner:

Start WTRB

Inputs Outputs

Node State

High Priority request Row# Actions Next state

* Initialization 0 Stop guard timer

Stop WTR timer

If RPL Owner:

Block RPL port

Unblock non-RPL port

Tx R-APS (NR, RB)

Else:

Block both ports

Stop Tx R-APS

B

A (Idle)

Local SF 1 Block failed port;Unblock non Failed port;

Tx R-APS(SF);

Flush FDB;

B

Local Clear SF 2 No action A

R-APS(SF) 3 Unblock non Failed port;

Stop Tx R-APS

If not “DNF” Flush FDB;

B

WTR Expires 4 No action A

WTR Running 5 No action A

R-APS(NR, RB) 6 Unblock non-RPL port A

R-APS(NR) 7 No action A

The R-APS request processing logic is defined in the format of a state machine.

R-APS Specific Information Format

R-APS information is carried within the R-APS PDU, which is one of a suite of Ethernet OAM defined in Y.1731

• Version – ‘00000’ – for this version of Recommendation

• OpCode – defined to be 40 in Y.1731

• Flags – ‘00000000’ – should be ignored by ERP

1 2 3 4

8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1

1 MEL Version (0) OpCode (R-APS = 40) Flags (0) TLV Offset (32)

5 R-APS Specific Information (32 octets)

.. …

37 [optional TLV starts here; otherwise End TLV]

last End TLV (0)

Defined by Y.1731 Defined by G.8032 Non-specified content

R-APS Specific Information Format

Specific information (32octets) defined by G.8032

• Request/State(4bits) – ‘1011’ = SF | ’0000’ = NR | Other = Future

• Status – RB (1bit) – Set when RPL is blocked (used by RPL Owner in NR)

• Status – DNF (1bit) – Set when FDB Flush is not necessary (Future)

• NodeID (6octets) – MAC address of message source node (Informational)

• Reserved1(4bits), Status Reserved(6bits), Reserved2(24octets) - Future development

1 2 3 4

8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1 8 7 6 5 4 3 2 1

Request /State Reserved 1 Status Node ID (6 octets)

RB

DNF

Status Reserved

(Node ID)

Reserved 2 (24 octets)

Link Failure (Normal to Protection)

2 3 4 5 61

SF

Normal

Protectionstate

failure

R-APS channel block

Client channel block

SF

A

RPL Owner

B

Message source

SFSF

CD

E

SFSFSF SFF

50 m

s

G

RPL

Flush Flush

FlushFlushFlushFlush

SFSF

SF

Failure Recovery

2 4 5 6

RPL

1

Normal

Protectionstate

recovery

failure

RPL Owner

B

SF SFSF

SF SF

F

A

E

NRNR

NRNR

NR, RPL Blocked

NR, RPL Blocked

NR, RPL Blocked

G

NRNR, RPL Blocked

NR, RPL Blocked

NR, RPL Blocked

D

Flush

FlushFlush

FlushFlush

50 m

sC

on

firm

atio

n

time

H

3

NR NR

C

R-APS channel block

Client channel blockMessage source

Flush

Reference

Ethernet Ring Protection Switching by the ITU

Telecommunication Standardization Sector (ITU-T) ITU-T Rec.

G.8032, 2008.

Ethernet Ring Protection for Carrier Ethernet Networks

by JEONG-DONG RYOO in Electronics and Telecommunications

Research Institute (ETRI), South Korea

technology brief ethernet ring protection switching (erps) april. 2010 d-link hq

Documents

erps slide

ethernet ring networks

erps stprstperps topology

ring protection link

ethernet traffic

ethernet layer

small ethernet switches

mature ethernet operations